This application claims priority under 35 USC 119(a) to Patent Application No. 2003-397480 filed in Japan on 27 Nov. 2003, the content of which is hereby incorporated herein by reference in its entirety.
The present invention relates to a heating apparatus which may be favorably implemented in a fuser apparatus for dry-type electrophotographic equipment, drying apparatus for wet-type electrophotographic equipment, drying apparatus for an inkjet printer, erasing apparatus for rewritable media, and the like; and to a control method for same as well as an image forming apparatus.
Frequently employed as fuser apparatus—this being one type of heating apparatus typically used in copiers, printers, and other such electrophotographic equipment—is a device of a type (the internally heated type) which is ordinarily constructed such that heating means comprising a halogen heater or the like is arranged within a fuser roller made up of a hollow core made of aluminum or the like, the halogen heater being made to generate heat and the fuser roller being set to a prescribed temperature (fusing temperature).
However, with this type of device, there has been the problem that the time following the start of heating until the fuser roller reaches fusing temperature, i.e., the warmup time, is long; and as it will also be necessary from the standpoint of user-friendliness to preheat the fuser roller during standby, electrical power consumption during standby is large.
In order to solve such problems, a fuser apparatus has been proposed (e.g., Japanese Patent Application Publication Kokai No. 2001-188427) of a type (the locally heated type) employing an upper roller (hot roller) having a four-layer structure comprising a core, an elastic layer, and a heat generation layer coated with a thin-film nonstick layer; heating of the upper roller taking place when inductive heating means (inductive heating coil) disposed in the vicinity of the exterior of the upper roller causes direct and local generation of heat by the heat generation layer of the upper roller.
This locally heated type of fuser apparatus has the characteristics listed at (1) and (2), below. (1) Because heat is generated directly by the heat generation layer, this being a thin metal sleeve (thickness on the order of 50μ) comprising Ni, SUS, or the like arranged at the outside circumference of the upper roller (hot roller), and because the nonstick layer on the surface thereof is formed so as to be extremely thin (silicone rubber; thickness on the order of 150μ), the thermal capacity of the upper roller (hot roller) is small, permitting reduction in warmup time.
(2) Because heat is produced at the outside circumferential portion of the upper roller (hot roller), thermal transfer characteristics and thermal supply characteristics relative to recording paper are excellent, as a result of which the need for heating means at the lower roller (pressure roller) is eliminated, simplifying constitution.
However, with the foregoing locally heated type of fuser apparatus, delivery of heat to the hot roller occurs in intensive and local fashion only in the vicinity of a zone in the circumferential direction of the hot roller which is directly below the inductive heating coil, and because the inductive heating coil is disposed adjacent to the hot roller, it would be difficult to arrange a temperature sensor such that it is able to press on the heat-generating portion of the hot roller in the region directly below the inductive heating coil. As a result, there has been the problem that the temperature measurement location of the temperature sensor is offset from the heating location of the inductive heating coil, and that this offset causes instability in temperature control.
Moreover, where the inductive heating coil is arranged so as to be more distant from the surface of the hot roller in order to make it possible for the temperature sensor to press on the heat-generating portion of the hot roller, not only has there been the problem of reduced efficiency in generation of heat by inductive heating, but there have also been problems such as occurrence of noise at the temperature sensor due to the effect of the magnetic field, occurrence of abnormalities during temperature control, and so forth.